1. Field of the Invention
The present invention relates to a welding apparatus, such as an arc welding apparatus for a welding robot system formed of a combination of a teaching playback type robot and a welding power source.
2. Prior Art
A prior art embodiment has a configuration shown in FIG. 4, as disclosed in Japanese Laid-open Patent Application No. Hei 9-85443.
First, the robot controller and the welding power source of the prior art embodiment are each provided with an analog command voltage value uniquely determined for a welding current command value, an analog command voltage value uniquely determined for a welding voltage command value and output characteristic curves for uniquely determining the respective values. Referring to FIG. 4, a welding current command signal i and a welding voltage command signal v are issued from a robot controller 101 to a welding power source 103 as analog voltage signals on the basis of their output characteristic curves via D/A converters respectively corresponding thereto. The analog command voltages are converted into digital data by the A/D converters of the welding power source 103, and a welding current command value and a welding voltage command value are obtained on the basis of the output characteristic curves, and taken in the welding condition control portion of the welding power source 103.
Next, the welding condition control portion carries out control to output an actual welding current and an actual welding voltage corresponding to the welding current command value and the welding voltage command value, respectively. At this time, for the robot, a movement target position is designated by teaching, and whether the target position having been designated by teaching is a welding position or not is determined by teaching. In addition, when the target position is a welding position, welding condition command values are also designated by teaching and stored as data in the memory inside the robot controller 101.
During robot operation, the welding torch of the robot 5 moves in accordance with the data designated by teaching and stored in the memory. When the welding torch of the robot 5 reaches the predetermined arc welding position, a welding current command voltage and a welding voltage command voltage, which are analog command voltages to be output to the welding power source 103, are obtained on the basis of the output characteristic curves of the welding current command and the welding voltage command in accordance with the data designated by teaching and stored in the memory. Binary data is then set and written to the buses of the D/A converters so that their desired command voltages are generated.
By this operation, the desired actual welding current and voltage are output to the welding power source 103.
Furthermore, as disclosed in Japanese Laid-open Patent Application No. Sho 63-119979, another prior art embodiment has a configuration wherein its robot controller must be provided with a hardware device for each condition to be commanded to the welding power source.
However, both the control portion of the robot controller 101 and the control portion of the welding power source 103 are digital circuits mainly composed of microcomputers. At the interface to the above-mentioned welding power source, the welding current and voltage command values, which are digital data, are D/A converted into analog commands, respectively, on the basis of their output characteristic curves, and transmitted from the robot to the welding power source. At the welding power source, the respective analog voltages are A/D converted into digital data on the basis of their output characteristic curves, and welding control is carried out.
Although the two control portions are digital circuits, analog circuits are present as described above, thereby causing conversion errors. This causes a problem wherein the welding current command value and the welding voltage command value transmitted from the robot are different from the welding current command value and the welding voltage command value received by the welding power source.
Furthermore, the prior art embodiment also causes a problem wherein the analog circuits are affected by drift because of changes in environment (temperature in particular) and changes with time.
In addition, in the case when the welding power source 103 or the robot controller 101 becomes faulty and at least one of them is replaced, welding confirmation adjustment comprising welding and condition calling must be carried out, even when the teaching data on the robot side is identical, because the individual analog circuits are slightly different from each other although there is no difference in model. This causes a problem of being unable to resume the operation of the robot welding system promptly.
Accordingly, the present invention is intended to provide a welding apparatus for an automatic welding line using a robot and a welding power source, comprising a digital communication control portion provided for each of the robot controller and the welding power source thereof, wherein welding current and voltage command values, which are digital data, are transmitted from the robot to the welding power source by digital communication, thereby excluding conversion errors because of the existence of the analog circuits of the prior art embodiment.